<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>CssFromJquery</title>
    <style type="text/css">
        .important
        {
            font-size: xx-large;
        }
        .blue
        {
            color: blue;
        }
    </style>
</head>
<body>
<p>
    This is a important test.
</p>
<h1>
    This text will get a kind of color!
</h1>
<button id="add">
    Add elements class
</button>
<button id="remove">
    Remove elements class
</button>
<script src="https://cdn.bootcss.com/jquery/1.10.2/jquery.min.js">
</script>
<script>
    $(document).ready(function () {
        $("button#add").click(function () {
            $("p").addClass("important");
            $("h1").addClass("blue");
        });
    });
</script>
<script>
    $(document).ready(function () {
        $("button#remove").click(function () {
            $("p").removeClass("important");
            $("h1").removeClass("blue");
        });
    });
</script>
</body>
</html>